July 2018 SW Climate Outlook - Monsoon Tracker
Assistant Research Professor, Arizona Institutes for Resilience
Assistant Professor of Anthropology, School of Anthropology
Ben McMahan joined CLIMAS after completing a PhD in Sociocultural Anthropology at the University of Arizona. His dissertation research was on hurricanes and disaster on the U.S. Gulf Coast, where he focused on
- Human interactions in dynamic social and environmental contexts,
- Risk perception and landscape changes during and after disaster, and
- Social network and policy responses to governance issues related to the acute threats of disaster; as they layer onto long term environmental issues and landscape scale changes.
He was also a key contributor to UA Bureau of Applied Research in Anthropology (BARA) collaborative/trans-disciplinary research on the social, economic, and environmental impacts of the US Oil and Gas industry (2007-2011), and the aftermath of the Deepwater Horizon oil spill (2010-2013).
At CLIMAS, his research activities included tracing how climate information is incorporated into regional decision maker networks, leading CLIMAS team research on the risks and effects of climate extremes, and collaborative research on the effects of climate variability on phenology and temporality of native plants in the region. He was also responsible for working to develop collaborative research opportunities and outreach efforts at CLIMAS, and as part of ongoing assessment and science/strategic planning, he contributed to strategic planning used to prioritize future research and outreach directions. He also coordinated publication of the monthly Southwest Climate Outlook, produced the Southwest Climate Podcasts, and was the online editor for CLIMAS’ blog - Southwestern Oscillations.
In 2008, the National Weather Service (NWS) changed the definition of the start of the Southwest monsoon from a variable date based on locally measured conditions to a fixed date of June 15 (and a fixed end date of Sept 30). Prior to 2008, the flexible start date reflected the seasonal progression of the monsoon, with a considerable temporal gradient across the region (Fig. 1).
In Southern Arizona, the monsoon start date was based on the average daily dewpoint temperature. Phoenix and Tucson NWS offices used the criteria of three consecutive days of daily average dewpoint temperature above a threshold (55 degrees in Phoenix, 54 degrees in Tucson) to define the start date of the monsoon (Fig. 2). Using that definition, the monsoon began in Tucson and Phoenix on July 8 this year. While an imperfect measure, this increase in dewpoint temperature contextualizes the slightly later-than-average start to monsoon activity compared to climatology, and roughly corresponds with upticks in precipitation activity across the Southwest (Fig. 3). Despite the relatively late start, the monsoon is now in full swing.
The seasonal totals to date (Fig. 4 on p. 5), the percent of normal precipitation (Fig. 5 on p. 5) and percent of days with rain (Fig. 6 on p. 5) all help characterize the spatial variability and intensity of the monsoon thus far. Tucson’s monsoon precipitation (p. 6) illustrates the amount of variability that can occur at a municipal scale.
Within the Tucson metropolitan region, an initial surge of activity associated with the remnants of Hurricane Bud brought considerable rainfall to the region June 15-17 (see last month’s Outlook for details). For much of the rest of June and the first week of July, however, there were few storms. Around July 8, rainfall picked up with widespread activity on a nearly daily basis, but with a wide range of daily totals from site to site (Fig. 7). Cumulative totals for the first month of the monsoon further reveal the extent to which some areas have received frequent and/or abundant precipitation, while others locations–often relatively nearby–have not (Fig. 8).
- Figure 1 - International Research Institute for Climate and Society - journals.ametsoc.org/doi/abs/10.1175/2007JCLI1762.1
- Figures 2-3 - CLIMAS: Climate Assessment for the Southwest - climas.arizona.edu
- Figures 4-6 - UA Climate Science Application Program - cals.arizona.edu/climate
- Figures 7-8 - CLIMAS: Climate Assessment for the Southwest - climas.arizona.edu Data: RainLog.org & Pima County Flood Control District